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            <h2 class="title" style="clear: both"><a id="nodurabletxn"></a>Non-Durable Transactions</h2>
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      <p>
            As previously noted, by default transaction commits are
            durable because they cause the modifications performed
            under the transaction to be synchronously recorded in 
            your on-disk log files.  However, it is possible to use 
            non-durable transactions.
        </p>
      <p>
            You may want non-durable transactions for performance
            reasons. For example, you might be using transactions
            simply for the isolation guarantee. 
            
            <span>
            In this case, you might
            not want a durability guarantee and so you may want to
            prevent the disk I/O that normally accompanies a
            transaction commit.
            </span>
            
        </p>
      <p>
            There are several ways to remove the durability guarantee
            for your transactions:
        </p>
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          <li>
            <p>
                    Specify          
                        <span>
                            <code class="literal">DB_TXN_NOSYNC</code> using the
                            <code class="methodname">DB_ENV-&gt;set_flags()</code>
                            
                        method. 
                        </span>
                        
                     This causes DB to not synchronously force any log 
                     data to disk upon transaction commit.  That is, the modifications are held entirely
                     in the in-memory cache and the logging information is not forced to the filesystem for
                     long-term storage.
                     Note, however, that the logging 
                     data will eventually make it to the filesystem (assuming no
                     application or OS crashes) as a part of DB's
                     management of its logging buffers and/or cache.
               </p>
            <p>
                        This form of a commit provides a weak durability
                        guarantee because data loss can occur due to
                        an application 
                        or OS crash.
                </p>
            <p>
                    This behavior is specified on a per-environment
                    handle basis.  In order for your application to exhibit consistent
                    behavior, you need to specify this 
                        <span>flag</span>
                        
                    for all of the environment handles used in your application.
                </p>
            <p>
                    You can achieve this behavior on a transaction by transaction basis by
                        <span>
                            specifying <code class="literal">DB_TXN_NOSYNC</code> to the
                                <code class="methodname">DB_TXN-&gt;commit()</code>
                                
                                
                            method.
                        </span>

                        

                </p>
          </li>
          <li>
            <p>
                    Specify
                    <span>
                        <code class="literal">DB_TXN_WRITE_NOSYNC</code> using the
                            <code class="methodname">DB_ENV-&gt;set_flags()</code>
                            
                        method. 
                        </span>

                        

                        This causes 
                        <span>
                            logging 
                        </span>
                        data to be synchronously
                        written to the OS's file system buffers upon
                        transaction commit. The data will eventually be
                        written to disk, but this occurs when the
                        operating system chooses to schedule the
                        activity; the transaction commit can complete
                        successfully before this disk I/O is performed
                        by the OS.
                   </p>
            <p>
                            This  form of commit protects you against application
                             crashes, but not against OS
                            crashes.  This method offers less room for the possibility of data loss than does
                            <span><code class="literal">DB_TXN_NOSYNC</code>.</span>
                            
                </p>
            <p>
                    This behavior is specified on a per-environment
                    handle basis.  In order for your application to exhibit consistent
                    behavior, you need to specify this 
                        <span>flag</span>
                        
                    for all of the environment handles used in your application.
                </p>
          </li>
          <li>
            <p>
                    Maintain your logs entirely in-memory. In this
                    case, your logs are never written to disk. The
                    result is that you lose all durability guarantees.
                    See 
                    <a class="xref" href="logconfig.html#inmemorylogging" title="Configuring In-Memory Logging">Configuring In-Memory Logging</a>
                    for more information.
                </p>
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